You’d think the people at Google had thought of everything by now. But not terribly long ago, they realized there was one idea they couldn’t quite wrap their heads around: how to build a more productive team.

To get to the bottom of this issue, they launched Project Aristotle. At its core, Project Aristotle studied the secrets of human interaction that led to more effective and productive small groups. Over several years, they interviewed hundreds of Google employees and analyzed data sets on more than 100 active internal teams.

The results were both stunning and heartwarming. They found that the best and most effective groups respected team member’s individual emotions and made an effort to get everyone to contribute to conversations equally. In a sense, they discovered that productivity in small groups had less to do with the people on a given team and far more to do with how those people treated and interacted with one another.

Project Aristotle’s findings showed that success and productivity more or less came down to understanding one another, finding ways to relate to one another, and individual employees being given space and opportunity to make themselves understood within the larger group. Instead of a top-down dynamic where people tried hard not to reveal what they didn’t know, the most successful groups featured members that encouraged one another to communicate and share questions and insights.

At the heart of most of these findings is the idea of “psychological safety,” a teamwork model in which members believe that it’s okay to take risks and share ideas without fear of rebuke or humiliation. As Google explains, “Did you feel like you could ask what the goal was without the risk of sounding like you’re the only one out of the loop? Or did you opt for continuing without clarifying anything, in order to avoid being perceived as someone who is unaware?”

The results of the study obviously resonated with the folks at Google. They now say psychological safety is the single most important factor when it comes to productive, effective, and successful teams.